It is well known to use pinned-photodiode arrangements where a single output amplifier serves more than one pixel, for example in the so-called 2.5T pixel where two pixels share a total of five transistors, or the 1.75T pixel where four pixels share a total of seven transistors. For color images, the pixels are overlaid with color filtering material, most commonly RGB. The arrangement which is most commonly used is the Bayer pattern where the pixels are BGBGBG . . . and GRGRGR . . . in alternate rows.
A problem with the Bayer pattern (and potentially also with other RGB sensors) is that with the materials typically used, green pixels are more sensitive than red and blue pixels because of the different color filter absorption coefficients. It would be desirable to reduce this difference by appropriate adjustment as between green and red/blue of exposure and/or gain, but this has not yet been accomplished.